Question

A particle is projected with velocity u at angle `theta` with horizontal. Find the time when velocity vector is perpendicular to initial velocity vector.
A. 4s
B. 2s
C. 3s
D. Not possible in this case.

Answer 1

Correct Answer - D
d. `vecu = 20 cos 30 hati + 20 sin 30hatj`
Now, `vecv = 20cos30hati`
`+(20sin30-"gt")hatj`

Let `vecv` be perpendicular to `vecu` at time t, then
`vec v * vecu = 0 rArr t = 4s`
Here time of flight, `T = 2s.` So it is not possible at any instant.